Upper Austrian industry specialist guarantees maximum system availability

Autor: Roland Gruber , 15.10.2018

A wealth of knowledge and experience, flexibility and the courage to innovate, are the hallmarks of the technological hydropower solutions produced by Braun Maschinenfabrik.

The Vöcklabruck hydrotech industry specialists began to react to the increased demand for horizontal rake systems a number of years ago and are now able to offer this variation with the superior technology Braun is known for today. The brand stands for technical sophistication, robustness and long-standing reliability. Proof of these qualities can be found working in numerous hydropower plants at home and abroad.

An enhanced degree of effectiveness due to the installation of new turbines and generators is a positive and desirable development. However, the corresponding effect on the system’s annual capacity can only be achieved if a constant and unhindered flow of water can be guaranteed. Combined flow-optimised fine rakes and an effective and reliable rake-cleaning machines are still some of the most important infrastructural components of a hydroelectric power station – be it a vertical or horizontal rake installation. Furthermore, the standard of driftwood and debris removal by the fine rake is usually influenced by the same three main factors for both vertical and horizontal set-ups – the gap between the blades or rods, the degree of turbulence in the pre-rake flow and by the thickness of the blades or rods. For these reasons, optimising the effectiveness of the fine rake set-up requires a wealth of theoretical knowledge and practical expertise.

An efficient engine of innovation
The trend towards the installation of horizontal rakes in new plants and revitalisation projects can be explained by the demands of fish ecology. Smaller gaps of 15 – 30mm between the blades lower flow speeds and enable the fish to free themselves from the inlet. Increased protection for fish is a key argument in favour of horizontal rake options. Never­theless, streamlined blade designs are commonly used to ensure efficient power station operation. A fully automated and reliable, high-performance rake cleaning machine ensures the maximum flow is constantly guaranteed across the entire cross-section of the rake. As recognised industry specialists, it is these attributes that have also helped to establish Braun Maschinenfabrik’s excellent reputation in horizontal rake technology. As a well-known non-stop engine of innovation this reputation has already spread far beyond the Austrian borders. The company’s list of references from the last few years provides some very convincing proof.

Reigning proudly in  Tyrol
One fine example of a system was installed at the Stanzertal power plant in the Tyrolean Oberland region, and went online in the autumn of 2015. Braun Maschinenfabrik supplied the weir gate, the overfill release gate and a horizontal fine rake for the side flow inlets of the water catchment system in Flirsch in the Arlberg region. The accompanying horizontal rake cleaning machine was designed to be robust and powerful, and even to remain fully operational during the expected periods of extremely low temperatures. Obviously, the system is also fully automatic and switches on when it senses a water level change of 5cm. After three years in operation the managers of the Stanzertal hydropower plant are very satisfied with the quality of the infrastructure supplied by Braun Maschinenfabrik.
A brand-new reference project is now going into operation in the Außerfern area of Tyrol. At the Höfen power plant, where the existing gates are being extended, the Vöcklabruck hydrotech industry business is also providing a flow-optimised horizontal rake and a high-performance rake cleaning machine. At the hydroelectric power plant in Reutte this offers benefits in terms of the fish ecology at the inlet – and as regards flood prevention. The intention is to implement the technical solutions required for relocation of the weir gates to avoid flooding in the Lech, as occurred in 1999 and 2005.

48 metres of precision
A brand new horizontal rake solution is currently being implement at another reference site on the River Traun in the Upper Austrian town of Laakirchen. The long-serving Danzermühl plant is now being completely rebuilt. At the time of writing (early 2018) building work is still underway. The sheer surface area of the rakes is impressive at a total of 240m². The whole rake is 48m long and 5m high. The rake blade gaps were a compromise between ecological requirements and the demand for energy production. In the upper section, the gaps are 45 mm and further down they are 30 mm. The construction consists of flat blades and round steel rods to form a framework of several rake units. The rake frames are all connected up and bolted on to 11 vertical rake carriers, which have also been designed to optimise water flow. A hydraulically driven horizontal rake- cleaning machine is used to keep the rake free of floating debris. This can be controlled fully automatically, by remote control signals or manually. As with the rake and the machine unit, the control system is also manufactured by Braun Maschinenfabrik.
Decades of expertise and experience have been augmented by a great deal of recent research and development to produce these fine-rake systems and rake cleaning machines. The horizontal rake systems are among the newer developments realised by Braun Maschinenfabrik, whose quality is now driving general industry trends.